In recent years, a number of medical devices have been designed which are adapted for compression into a small size to facilitate introduction into a vascular passageway and which are subsequently expandable into contact with the walls of the passageway. These devices, among others, include blood clot filters which expand and are held in position by engagement with the inner wall of a vein, such as the vena cava. These vena cava filters are generally designed to remain in place permanently. Such filters include structure to anchor the filter in place within the vena cava, such as elongate diverging anchor members with hooked ends that penetrate the vessel wall and positively prevent migration in either direction longitudinally of the vessel. The hooks on filters of this type are rigid, and within two to six weeks after a filter of this type has been implanted, the endothelium layer grows over the diverging anchor members and positively locks the hooks in place. Any attempt to remove the filter results in a risk of injury to or rupture of the vena cava.
A number of medical procedures subject the patient to a short-term risk of pulmonary embolism, which can be alleviated by a filter implant. In such cases, patients are often averse to receiving a permanent implant, for the risk of pulmonary embolism may disappear after a period of several weeks or months. However, most existing filters are not easily or safely removable after they have remained in place for more than two weeks, and consequently longer-term temporary filters that do not result in the likelihood of injury to the vessel wall upon removal are not available.
It is believed that most of the known filters are not capable of being delivered without regard for the orientation of the filter or access site. It is also believed that most of the known filters are not capable of being retrieved in either one of a femoral or jugular approach with one retrieval device.
One of the known filters, described and shown in U.S. Pat. No. 6,251,122 issued to Tsukernik, utilizes a plurality of strands with a sliding member slidingly disposed about a portion of the strands. Recovery of this filter, however, is believed to require two different devices approaching from both the femoral and jugular access sites as shown in FIG. 4 of this patent.
Another known filter, described and shown in U.S. Pat. No. 6,443,972 as a somewhat symmetrical filter. However, this filter, like others, can only be retrieved from one access site.
Applicants have recognized that biological anatomies may vary such that access from the jugular may be inappropriate or that access from a femoral site is similarly inappropriate. For example, in the known filter delivery system, if the jugular (or femoral) site is inappropriate for delivery and the delivery system of a known filter can only be utilized from the jugular (or femoral) approach then the clinician would have to obtain a femoral (jugular) delivery system. To provide immediate access to an alternative delivery device during a procedure, this would require the clinician to have two systems in the clinical inventory prior to the procedure. Similarly, in the known delivery system, if the retrieval is inappropriate for the jugular (or femoral) approach then the clinician would have to obtain a femoral (or jugular) retrieval system prior to the procedure. Immediate access to one or the other retrieval systems would require a clinical inventory of two different retrieval systems prior to the procedure. Hence, applicants have recognized the desirability for a blood filter system that addresses one or more of the above issues.